This invention relates to roadway guardrail systems, and more particularly, to guardrail barriers.
Guardrail barriers are positioned along roadways to prevent or reduce the damage to vehicles and to their occupants when they leave the roadway. The guardrail barriers are designed to redirect the vehicle back onto the roadway and to absorb energy in a controlled manner from the vehicle. The barrier is supported on posts or the like and may have different amounts of flexibility depending on its design. It provides an effective depth or capture area intended to receive the moving vehicle in a recessed portion of the guardrail barrier bounded by upper and lower curved portions projecting toward the roadway to stabilize the vehicle and reduce the tendency for the vehicle to vault over or dive under the barrier or to roll when redirected by holding the vehicle against upward and downward motion. The barriers should be positioned with the lower peak of the curved portions no higher than 20.5 inches from the ground. Terminals are located at the ends of the guardrail system's barrier to receive vehicles that hit at the end. The terminals and the barriers work together to absorb energy when the terminal is hit.
While prior art barriers differ one from the other and have many types of designs, the most common type of prior art barrier in the United States is a W-Beam, galvanized versions of which are dimmensioned to have an area of its cross sectional edge of 1.99 square inches (in..sup.2), a thickness of its edge of 0.1046 inches (in.), a gauge of 12, a depth from the top edge vertically down to the bottom edge of 12.25 inches, an effective depth from the centerline of the uppermost curved portion of the barrier (horizontal radius) to the centerline of the lowermost curved portion (horizontal radius) of 7.63 inches, a width (from vertical plane touching the barrier at the point farthest from the road center to vertical plane touching barrier nearest road center--i.e. peak of positive curve to peak of negative curve) of 3.35 inches.
This standard W-beam has an Xbar (distance from lower edge vertically to centroid) of 6.13 inches, a Ybar (distance from peak of positive curve to centroid) of 1.69 inches, an Ix (vertical moment of inertia) of 29.65 in..sup.4, a horizontal moment of inertia, Iy, of 2.32 in..sup.4, an Sx (vertical section modulus) of 4.84 in..sup.3, an Sy1 (horizontal section modulus at positive peak) of 1.38 in..sup.3, an Sy2 (horizontal section modulus at negative peak) of 1.40 in..sup.3, a length (length of edge of a section if it were straight) of 19 inches, and a weight per length of the barrier of 6.77 pounds per foot. The outer curved portions of standard w-beams are each symmetrical about a horizontal line through its peak. Usually, sections of w-beams are spliced together by eight bolts, one row of four bolts on each side of the post bolts, evenly spaced so that two of the four are on the outer section of the peak of each outer curve and two on the inner section.
Barriers with these dimmensions operate well on some vehicles but have several disadvantages as to other vehicles, such as for example: (1) they provide so much resistances to high center of mass vehicles that, under an undesirably large number of circumstances, they cause the center of mass to rise to a height over the vertical, resulting in the vehicle rolling or vaulting over the guardrail; and (2) certain vehicles with a high center of mass and high bumper mounting heights are not captured by the prior art W-beam guardrails. Thus, certain light trucks, such as pick-ups, vans and sport-utility vehicles may be caused to roll and sometimes vault over the guardrail barrier. However, the W-beam barrier cannot be raised because small cars would wedge under the railing and snag on the guardrail posts.